1. Field of the Invention
This invention relates to surgical instruments, and more particularly to surgical instruments used to bite out or cut portions of bone or cartilage.
2. Description of the Related Art
Rongeurs are surgical instruments for the cutting away of human tissue, and most commonly, cartilage and/or bone. At present there is a need for a rongeur having a less cumbersome and less intrusive foot plate which would make the instrument safer for use in the spinal canal and about the delicate neural structures and extend the range of use of the instrument by allowing it to be used in closer proximity to those same structures.
Attempts have been made in the past to provide a rongeur with a less cumbersome foot plate. For example, U.S. Pat. No. 4,990,148 issued to Worrick, III et al. ("Worrick") on Feb. 5, 1991 teaches a means for allowing a limited reduction of the foot plate thickness by the addition of a groove placed at the junction of the foot plate to the shaft for the purpose of relieving crossed fields of stress. However, the foot plate of Worrick is still internally cupped to maintain a cutting edge, which thus limits any further reduction in the thickness of the foot plate.
Essentially flat foot plates had been in use earlier this century, but proved to be undesirable because spinal bone is markedly compressed during the biting process. When the foot plate is flat, the mass of bone bitten is forcefully compacted into the singularly cupped recess of the movable jaw such that it is extremely difficult to remove that bone after each bite.
At present, there is also a need for a rongeur with a capacity to remain within the wound and to repeatedly bite and to store the bone bitten until all the requisite bone removal has been completed without the need to continuously remove the rongeur from the wound for the purpose of removing the bone from the instrument to clear the cutting edges. A further and related need is for a rongeur that would collect and contain all of the bitten material such that the delicate neural structures would be protected from contact with the bitten material and/or any cogenerated inadvertent debris. In this regard, any rongeur can bite more than once, but not properly. That is, one could deliberately take several small bites, each of which would fail to fill the cup in the foot plate and the singularly cupped recess of the moveable jaw, in lieu of taking one full bite. However, once the cup and the cupped recess are filled further biting is not possible. Bone may be crushed as cups that are already full approach one another, but their contents will shield any further interposed bone from the cutting edges, thus making any further bone cutting impossible.
An example of a multibite rongeur is shown in U.S. Pat. No. 3,902,498 issued to Niederer on Sep. 2, 1975. Niederer teaches the use of a rongeur hollow at the tip such that it is possible to take several bites. Unfortunately, since the hollow tip is open to the wound at both ends, the further use of the instrument pushes the already bitten material out of the other end of the hollow tip and back into the depths of the surgical wound where it can cause great harm.
Finally, there is also a need for a surgical rongeur that will upon each use present a perfectly formed and razor sharp cutting edge, which will mate exactly, and close completely, to the opposed foot plate. In this regard, Niederer taught the use of a disposable cutting element but not the use of a disposable storage chamber for the cut pieces.
Of note is U.S. Pat. No. 5,026,375 issued to Linovitz et al. on Jun. 25, 1991 which claims a modification of Niederer's teaching wherein the tip is replaceable rather than disposable, in that it requires assembly and is secured with a screw, and wherein the tip has extending from its lower surface an inverted "T" shaped portion made to be inserted into and engage with a correspondingly internally disposed inverted "T" slot within a portion of the instrument shaft.
A further problem with the design of conventional rongeurs limiting further thinning of the foot plate so as to maintaining adequate strength is that since the opening of a conventional rongeur is much greater in its capacity than the sum volume of its cuts, in the process of biting with such a rongeur, the bone is not only bitten but is further compacted under tremendous pressure, that pressure being transmitted directly to the foot plate.
Conventional rongeurs by design have excursions beyond that needed to merely close the jaw completely when the rongeur is new. That is because the manufacturer must allow for the wear that will occur at the cutting edges, and yet still provide for the capacity of the instrument to still close fully later. Thus, when bone is bitten with a conventional rongeur, a force considerably greater than that necessary to cut or even compact the bone is additionally transmitted to the foot plate as the slidable member attempts further proximal migration in opposition to the foot plate.